The goal of this application is to understand the processing and coding of natural taste stimuli by gustatory receptor cells that are housed in taste organs on the mouthparts of an insect model. Gustatory receptor cells constitute a sensory filter for environmental taste signals and in insects, they transfer information about taste stimuli directly to taste centers in the brain. Therefore, gustatory receptor cells form the first layer of a decision making process that ultimately determines whether food is accepted or rejected by the animal. The major premise of this research is that we know very little about the neural mechanisms that underlie feeding, specifically the ultrastructural organization of the taste apparatus, the neural coding of taste stimuli, or the feeding behavior evoked by these stimuli. The gustatory organs of caterpillars provide an excellent system to address questions about the taste system. These organs form a relatively simple sensory system. Two gustatory organs, each with four putative gustatory receptor cells, are thought to respond to stimuli in different behavioral or ecological contexts. However, taste stimuli can be fairly complex because they can be composed of multimolecular mixtures. The animal faces the task to decipher individual tastants and then to make an appropriate feeding choice. Our research strategy is to first describe the cellular and subcellular organization of taste organs and receptor cells therein. In a second step, we will use feeding behavioral bioassays to test which taste stimuli evoke feeding or food rejection. In a third step, we describe the neural responses of gustatory receptor cells to selected individual taste stimuli, as well as to mixtures, and will correlate the neural and behavioral responses. These studies will provide insights into peripheral taste processing from molecules to behavior in an unprecedented manner.